chromatography 3.3.16 in papers 2 + 3
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what are the types of chromtography?
• thin layer • gas • column
what is thin layer chromotography?
a plate is coated with a solid and a solvent moves up the plate
what is column chromotography?
a column is packed with a solid and a solvent moves down the column
what is gas chromotography?
a column is packed with a solid or with a solid coated by a liquid, and a gas is passed through the column under pressure at high temperature.
what is the mobile phase?
• the solvent • in gas chromotogrpahy an inert gas
whata the stationary phase?
• a solid, chromotography paper • in gas chromotogrpahy its a liquid on inert solid
hows does a solid and liquid stationary phase seperate?
• A solid stationary phase separates by adsorption • A liquid stationary phase separates by relative solubility
what does seperation depend on?
the balance between solubility in the moving phase and retention in the stationary phase.
if the sample is polar and the solvent was also polar what does this mean?
sample will travel faster than non-polar molecules
outline how to do chromotography
• draw a pencil line 1 cm above the bottom of a TLC plate and mark spots for each sample equally spaced along line. • Use a capillary tube to add a tiny drop of each solution to a different spot and allow the plate to air dry. • Add solvent to a chamber or large beaker with a lid so that is no more than 1cm in depth • Place the TLC plate into the chamber, making sure that the level of the solvent is below the pencil line. Replace the lid to get a tight seal. • When the level of the solvent reaches about 1 cm from the top of the plate, remove the plate and mark the solvent level with a pencil. • Place the plate under a UV lamp in order to see the spots. • Draw around them lightly in pencil. • Calculate the Rf values of the observed spots.
when is 2 directional chromotogrpahy done?
• if components in the mixture have the same Rf value • if some components are not soluble in the first solvent
how is column chromotogrpahy carried out?
• A glass tube is filled with the stationary phase usually silica or alumina in powder form to increase the surface area. • A filter or plug is used to retain the solid in the tube. • Solvent is added to cover all the powder. • The mixture to be analysed is dissolved in a minimum of a solvent and added to the column. • A solvent or mixture of solvents is then run through the column. • The time for each component in the mixture to reach the end of the column is recorded